package com.app.protocol;

/**
 * CRC8协议助手
 * 
 * @author fanpei
 *
 */
public class CRC8Util {

	/**
	 * 描述表
	 */
	private final static char dscrc_table[] = { 0, 94, 188, 226, 97, 63, 221, 131, 194, 156, 126, 32, 163, 253, 31, 65,
			157, 195, 33, 127, 252, 162, 64, 30, 95, 1, 227, 189, 62, 96, 130, 220, 35, 125, 159, 193, 66, 28, 254, 160,
			225, 191, 93, 3, 128, 222, 60, 98, 190, 224, 2, 92, 223, 129, 99, 61, 124, 34, 192, 158, 29, 67, 161, 255,
			70, 24, 250, 164, 39, 121, 155, 197, 132, 218, 56, 102, 229, 187, 89, 7, 219, 133, 103, 57, 186, 228, 6, 88,
			25, 71, 165, 251, 120, 38, 196, 154, 101, 59, 217, 135, 4, 90, 184, 230, 167, 249, 27, 69, 198, 152, 122,
			36, 248, 166, 68, 26, 153, 199, 37, 123, 58, 100, 134, 216, 91, 5, 231, 185, 140, 210, 48, 110, 237, 179,
			81, 15, 78, 16, 242, 172, 47, 113, 147, 205, 17, 79, 173, 243, 112, 46, 204, 146, 211, 141, 111, 49, 178,
			236, 14, 80, 175, 241, 19, 77, 206, 144, 114, 44, 109, 51, 209, 143, 12, 82, 176, 238, 50, 108, 142, 208,
			83, 13, 239, 177, 240, 174, 76, 18, 145, 207, 45, 115, 202, 148, 118, 40, 171, 245, 23, 73, 8, 86, 180, 234,
			105, 55, 213, 139, 87, 9, 235, 181, 54, 104, 138, 212, 149, 203, 41, 119, 244, 170, 72, 22, 233, 183, 85,
			11, 136, 214, 52, 106, 43, 117, 151, 201, 74, 20, 246, 168, 116, 42, 200, 150, 21, 75, 169, 247, 182, 232,
			10, 84, 215, 137, 107, 53 };

	/**
	 * 获取数据CRC8校验码
	 * 
	 * @param srcCrc 初始crc
	 * @param datas
	 * @param start  起始校验位置
	 * @param len    从0开始指定的长度长度
	 * @return
	 */
	public static byte getCRC8(byte srcCrc, byte[] datas, int start, int len) {
		byte crc = srcCrc;
		if (datas != null) {
			int off = 0;
			for (byte b : datas) {
				off++;
				if (off - 1 < start)
					continue;
				crc = (byte) dscrc_table[0x00ff & (crc ^ b)];
				if (off - start == len)
					break;
			}
		}
		return crc;
	}

	/**
	 * 获取数据CRC8校验码
	 * 
	 * @param datas
	 * @return
	 */
	public static byte getCRC8(byte srcCrc, byte[] datas) {
		byte crc = srcCrc;
		if (datas != null) {
			crc = getCRC8(srcCrc, datas, 0, datas.length);
		}
		return crc;
	}

	/**
	 * 获取数据CRC8校验码
	 * 
	 * @param datas
	 * @return
	 */
	public static byte getCRC8(byte[] datas) {
		return getCRC8((byte) 0, datas);
	}
}
